Hardening material resistant to heat, acid, corrosion, and abrasion, and method of producing the same



Patented Aug. 3, 1937 UNITED STATES HARDENING MATERIAL RESISTANT TO HEAT, ACID, CORROSION, AND ABRASION, AND METHOD OF PRODUCING THE SAME Norman w. Cole, Whittier, and Walter 11. Ed-

monds, Dos Angeles, Calif.

No Drawing. Application June 29, 1933, Serial No. 678,260

. 13 Claims.

Our inventions relate to resistant material; material that resists abrasion, corrosion, acids, and heat, and are particularly directed to new and useful compositions of matter having chromium and boron as important constituents.

In general terms, our inventions may be outlined as including: first, the new composition of matter having the formula CrBa; second, the method herein disclosed for producing said composition together with certain concomitant materials, largely CH3 and CraBa; third, novel and useful compositions of matter incorporating said composition of matter or said concomitant materials either with or without said composition first mentioned; and, fourth, methods of producing and utilizing compositions of matter that incorporate said composition of matter in combination with one or more of said concomitant materials and other added materials.

The features peculiar to our invention, and the objects and advantages of our invention may best be understood by reference to the following detailed description covering thefour aspects recited above.

The chemical compound of chromium and boron having the formula CrIBz has, to our knowledge, never been found in nature, nor, heretofore, been described in literature as compounded and isolated in the laboratory. Our experiments at the present state indicate that the final product, CrBz, has a brownish color, a crystal construction probably of the tetrahedral system, a specific gravity of approximately 4.2 to 4.55, and a hardness of approximately 8.5 or higher, Mohs scale. We have found the crystals to be insoluble in sulphuric acid, hydrochloric acid, nitric acid, and potassium hydroxide; but the crystals will slowly dissolve in hydrofluoric acid to form a light green solution; and they are readily brought into solution after fusion with sodium peroxide in a nickel crucible. We have exposed these CrBa crystals to as high a temperature as 1350 centigrade without causing the crystals to fuse and with no indication of oxidation. Fusion has been accomplished, however, by means of an electric arc. v

CrBz as produced by our process is a granular.

material that may be used as an abrasive in loose form for grinding and polishing surfaces; The ClBz crystals may also be incorporated in a suitable hinder or matrix, as sodium silicate, shellac, rubber, or bakelite, to form grinding wheels for various purposes. The ClBz crystals may be incorporated in a metal body to increase the hardness and tensile strength of the body, or may be associated with the surface of the metal body to resist abrasion, corrosion, acids or heat. For such purpose, the crystals may be incorporated in the body of metal by mixing the crystals with the comminuted metal, heating the mixture above the melting point of the metal and thencasting the resultant; or the crystals may be mixed with comminuted metal to form a briquet that may then be fused by heat into a coherent body particularly suitable for a cutting or drilling tool.

The Cl'Bz crystals may be applied to the surface of a metal body in various ways. For instance, the crystals may be applied with an adhesive to the interior walls of a mold in which metal is subsequently poured; or the crystals may be superficially embedded in the surface of metal heated to a suitable molten state; or, as will be further explained later, the crystals may be incorporated in a matrix suitable for fusion with the surface of a metal body.

To produce an acid-resistant surface on any body, the CrB; crystals may be incorporated in a suitable carrier for painting the surface, or, preferably, the surface will first be covered with a suitable adhesive coating against which the CI'Ba crystals in a finely divided state will be sprayed in profusion. Other applications of CrBz, based upon its useful characteristics, will readily occur to those versed in the arts related to our inventions.

We have discovered that our preferred process is of special value in that it produces with CrIBa certain concomitant materials peculiarly adapted to constitute a matrix in the very form in which they are produced. In fact, our process may be carried out in a sequence of steps to create the CiBz crystals and the concomitant matrix concurrently, the CrBa crystals being thereby distributed uniformly in the matrix and intimately associated therewith.

This product, CI'Bz, and the concomitant matrix unified therewith, is now known by the trade-mark Colmonoy, and is usually produced in granulated form, each granule comprising minute crystals of CrBz, of the order of .001 inch in length, embedded in a mass of united crystals of the concomitant matrix, the matrix crystals being .005 to .02 inch in length. The process may stop with the production of the "Colmonoy crystals, or further steps may be taken for the purpose of isolating the CrBz crystals therefrom.

Our preferred mixture for the alumino-thermic reaction comprises:

Per cent Chromic anhydride CrOa 46.25 Boron trioxide B20: 16.25 Powdered aluminum 37.50

When this mixture is ignited in a crucible, an exothermic reaction proceeds violently to the bottom of the crucible where a molten mass accumulates and cools to a solid conglomerate body heneath a crust of slag and aluminum in free and compounded state.

Besides CrBz, Cr]; and CrsBz, this conglomerate may contain chromium, boron, and aluminum, these latter being in free, compounded or alloyed state. Under the usual conditions of manuiac ture, iron also is usually introduced into this re= sultant. I

To reduce this conglomerate to a more uniform material, narrowed down to the constituents pertinent to our invention, the solidified material is then crushed, pulverized, washed, and treated with a suitable acid, such as hydrochloric acid of specific gravity 1.1. Preferably, the diswtion in the acid is extended over a period of ten or twelve hours. The residue, amounting usually to '75 to 80% of the original conglomerate, consti tutes the so-called Colmonoy" crystals. It may be noted here, thatthe crushing anolpulverizine operations may be eliminated by simply exposing the conglomerate body to the atmosphere for several weeks, such exposure causing the body to disintegrate into a finely divided mixture of Gel money crystals and other material. The discs tion in hydrochloric acid may also be omitted, since the associated products such as aluminum, chromium and boron in free and compounded state do not interfere with some applications of our invention.

It is to be understood that included within our invention is the material produced by carrying out the. above described process up to the point of the treatment with hydrochloric acid. in other words, our invention includes'the powdered conglomerate which usually, as suggested alcove, is refined, as by acid treatment, to prmuce the so-called Colmonoy crystals.

- This "unrefined material is formed from chromlmn, boron and aluminum. The percentages of these elements in the unrefined material depend somewhat upon the nature of the tool or other body to which the unrefined material is to be 40 applied, as well as upon the intended use of the tool or body. The following table shows what we now consider the practicable limits of the percentages of these elements:

Per cent Chromi m dc to $5 Boro 5 to Aluminum v 1 to 25 A very satisfactory unrefined material, and one tains these elements in the following percentages:

that we now' prefer for general purposa, con- Per cent Chromi m 6t Boron 27 Aluminum 10 The precise constituents of Colmonoy crystals vary with the proportions of the original mix, the

purity of materials used, and the efiiciency or the refining. process. A typical finding by "indirect analysis" in the laboratory is as follows:

From a. number of such analyses we have concluded that the ranges oi variation oi the three 75 important constituents are:

Per cent CrBe l- 3 Cit-B x 1 50-90 Cr Be 10-40 "The CrBz crystals may be isolated as a residue by boiling the Golmonoy crystals in sulphuric acid oil specific gravity 1.3 under a reflex condenser for twelve to seventy-two hours. The sulphuric acid dissolves the CrB, Cl'aBz and other of what we term concomitant materials contained in the Colmonoy crystals.

A sample oi these insoluble crystals produced under the conditions of commercial manufacture was analyzed as follows:

Percent Chromium 3515 Boron 29.95 Aluminum 15.32 time 17.44.

A further study oi the same sample indicated that-the elements were A second sample produced with unusual care in the laboratory was assayed as follows:

\ Per cent Chromium 68.78 Enron 29.22 Aluminum 1.11 liron 2.66

Further study of this second sample indicated that the elements were combined as follows:

Per cent @rEs 97.30 Feh 3.17 Ame .47 A195}: 1.56

The important conclusion to be drawn from these analyses is that there is a sufiicient quantity of boron present to account for CrB-z and additionally to account for the FeB and MB: present. The iron in the analyses above is accounted forby impurities in the commercial ingredients such as scale and rust from containers.

It is possible, with care, as indicated above, to reduce the proportion of the iron and aluminum in the so-called concomitant materials. We have not found it necessary, in commercial practice, to keep this proportion down; and, moreover, these materials so readily combine with CrB and Cl'aBz inthe Colmonoy crystals and so readily blend with CIB: when CrB and C133: are dissolved out of Colmonoy crystals, that we do not regard them as undesirable impurities. On the contrary, further experiments are projected to explore the possibility that one or more of these concomitant materials may have functions in our inventions that may be identified.

present in the following We do know that the Colrnonoy crystals are of crystal structure, 1. e., that the individual crystals of CrBz are interspersed in a matrix comprising mostly united crystals of CrB; and the matrix may be in part or in total in the nature of a solid solution.

It is obvious that the structure and'the composition of the Colrnonoy crystals will be affected by the proportions of the original mix, as well as the conditions surrounding the above described process. If the proportion of aluminum specified in our preferred mixture above is substantially reduced, the alumino-thermic reaction will be incomplete; if the proportion of aluminum is substantially increased, then the proportion of aluminum combined with other elements in the Colmonoy crystals will be increased. Experiments indicate that the proportion of CrB-z in the Colrnonoy crystals may be 1 increased by increasing the intensity and duration of the reaction, or by increasing the proportions of B203 and aluminum in our mix. The size of the C115: crystals probably may be increased by carrying out the reaction under pressure and causing the molten product to cool over a more extended period of time.

The significance and importance of our preferred mixture may be understood by considering the atomic relationships involved, calculating the heat produced, and studying the effect of substituting ClzOs for CrOa.

The reaction produced by a mixture comprising chromic anhydride 46.25%,- boron trioxide 16.25%, and powdered aluminum 37.50%, is represented by the equation:

By substituting heatsof formation in the usual manner, it may be computed that this reac- 40 tion produces 644,400 calories. If the heat capacities of the products are used, leaving chromium and boron in the elementary states (since no data on the heat of formation of chromium borides is available) a theoretical temperature 45 of approximately 13,900 F. is found. Now, an ordinary Thermite reaction with iron oxide develops an actual temperature that is approximately 68 per cent of its theoretical temperature calculated as above. Applying the same correc- 50 tion to the theoretical temperature l3,900 F., a

temperature of approximately 9400 F. is indicated.

If Cl'zOs is substituted for .CrOa to obtain the same quantities of chromium and boron in the 55. reaction, thus:

the "probable temperature produced is only 5090 F.

This comparison emphasizes the importance of the particular oxide selected. The mixture corresponding to the second equation is not operative, since it fails to produce a temperature sufliciently high to form CIBz. From experience 65 with various reactions applicants have concluded that a temperature substantially in excess of 7000" F. isrequired to produce Cl'Bz.

The unusual resistance to abrasion that characterizes the Colrnonoy crystals may be explained 70 in part by considering certain facts. In the first place, the incorporated Cl'Bz crystals distributed throughout the body and surface of the matrix are extremely hard and refractory; second, we have the combination of the abrasive CrBa crys- 75 tals with a crystalline matrix, which matrix is itself resistant to wear; third, by virtue of the CrBz crystals and the crystalline matrix being formed concurrently, the two are more intimately associated than is possible in a product obtained by merely mixing an abrasive into a matrix; fourth, because the CrBz crystals and the crystalline matrix are formed in a fluid condition and both remain fluid until the mixture drops below the melting point of the CI'Bz crystals, and because the violent reaction thoroughly agitates the intermixed crystals in fluid state, the CrB: crystals are uniformly distributed throughout the matrix; and, fifth, the CIB: crystals, as produced by our method, are extremely small and, therefore, are not as readily disioined from the matrix as would be the case were the CrBz crystals relatively large.

It will be noted that the above features relate to the physical structure of the Colrnonoy crystals. In other words, the combination of ClBz and the matrix is particularly effective because of the abrasive-resistant character of the CrBz crystals and the matrix, because of the exceptional bond between the two, and because of the minute size of the CrBz crystals.

In developing our invention, we have discovered that in addition to. serving strictly as a matrix for the CrBz crystals, the concomitant materials in Colrnonoy crystals may have important roles in combining ClBz crystals with other substances for various purposes. For instance, it has been stated above that the isolated CrBz crystals may be incorporated in a metal body by mixing the crystals with the comminuted metal and then heating and casting the metal. Such a combination is not readily achieved, because the CrB; crystals tend to float on the surface of a heavy metal bath in a manner not conducive to uniform distribution through the metal, and the crystals that do enter the molten metal do not have the desired intimate association with the metal body. If the Colrnonoy crystals, i. e., ClBz mixed with CrB, ClaBz and other concomitant materials, are

intermixed with the comminuted metal, the desired results are readily achieved. Usually the CrB, CraBz and the other concomitant materials in molten state enter into solid solution or chemical combination with the metal as the metal cools, whereas the CrBz maintains the crystal form throughout. Since the melting point of CrBz is substantially above that of a heavy metal, the CrBz maintains its crystal form while the metal is still fluid, with the result that the crystals are in close bond with the metal when the entire mixture solidifies.

It is apparent, then, that CrB, CraB and the other concomitant materials serve, in effect, as a flux promoting the incorporation of CIBz into the metal body and facilitating uniform distribution of the CrBz crystals throughout the metal body. When the mixture cools; the fact that the concomitant materials, including CrB and ClaBz, have a physical arlinity for the CrBz crystals, and a tendency to enter either into chemical combination or solid solution with the metal, insures the intimate association of the ClBz crystals with the metal. The presence of these component materials brings about a finer grained and more coherent solid than we have been able to obtain in their absence.

We have reason to believe that'this excellence of grain is promoted by the fact that the refrac tory ClBz crystals in the moltenbath of concomitant materials and metal serve as nuclei of crystallization; by virtue of the so-called "flux action" of the concomitant materials, these countless nuclei are evenly distributed, hence the fine grain of the solidified product. The concomitant materials, together with the Cl'Bz crysv tals in a metal body, constitute a combination in which each element has a function bearing on the result produced by the combination.

It will be noted that the important effects stance, and the surface then subjected to the heat of a welding torch, the concomitant products may be fused into the metal body, forming with the embodied CrBz crystals an outer layer integral with the metal body. Because of the resistant character of CrBsin combination with the matrix of concomitant materials, such a procedure constitutes, in efiect, a superior process of casehardening.

The development of this aspect of our invention, i. e., the peculiar effectiveness of adding the concomitant materials to combinations of ClBz with other metals, may be appreciated by considering illustrative compositions of matter.

The proportion of Colmonoy crystals to the metal or alloy body, as well as the particular alloy to be used, will depend upon the particular purpose in view, intelligent variation being within the skill of the artisan. Generally speaking, the

.0 higher the degree of hardness, or resistance to corrosion, acid or. abrasion required, the higher the percentage of Colmonoy crystals employed.

For example, where toughness is the most important of the characteristics desired in the prod- 45 uct, the percentage of the Colmonoy crystals may be as low as 12%, whereas a cutting tool to be used on a lathe or for drilling may incorporate 90% of Colmonoy crystals.

A tough cutting tool having a low melting point 50 may be constituted as follows:

. v Per cent Colmonoy crystals 12 to 16 Tungsten, comminuted 12 to 18 Iron, comminuted 68 to 76 55 When these constituents are melted in a crucible, and then allowedto cool, the ClBz crystals will be uniformly distributed throughout the solid mass, while the concomitant materials in the 6b Colmonoy crystals will alloy or otherwise combine with the tungsten and iron.

An exceedingly hard tool, highly resistant to abrasion and acids, and having a high melting point, may be constituted as follows:

65 Percent Colmonoy crystals 75 to 90 Nickel, comminuted to 25 Here, again, the concomitant materials alloy or otherwise combine with the nickel, while the 70 CrBs crystals remain unaffected.

A method has heretofore been described of producing an extremely resistant material by heating a briquet of powdered metal and CrBz. gSuch abriquet is held together by fusion'of the 75 metal alone, the crystals simply being trapped placed on the surface of a steel body, for in- Percent Colmonoy crystals 6 Nickel, comminuted. 19 Steel, comminuted 75 The use of Colmonoy crystals to produce a re-: sistant facing on metal bodies may be appree elated by considering illustrative procedures.

The application of Colmonoy crystals to a steel tool by fusion has already been mentionedf Contrary to the usual method of case-hardening, our procedure of fusing Colmonoy; crystals to the face of a steel body may be arranged to avoid introducing carbon into the body. This fact is important when it is desirable to retain in a metal base the toughness characteristic of a mild steel having a low carbon content. We have found .that when the colmonoycrystals are fused to the surface of a mild steel body, the matrix of the concomitant materials actually draws carbon from the steel body, and that the carbon so derived may actually increase the hardness of the matrix that coats the steel body.

It should also be pointed out at this point that the Colmonoy crystals are so light that one pound will cover an exceptionally large area, roughly, three times the area that will be covered with the equivalent weight of tungsten carbide.

In addition to the simple procedure of fusing Colmonoy crystals to the surface of a metal, a case-hardening" may be achieved by various other procedures. For instance, the matrix of the surfacing composition may include a metal ,in addition to the so-called concomitant materials of the Colmonoy crystals. In such case, the Colmonoy crystals may be first combined with the metal to make a solid material suitable for surfacing tool steel, and then this solid material may be fused to the surface of the tool steel. Nickel may be so used as a constituent in the matrix of the surfacing composition. The combination of Colmonoy crystals with nickel, cobalt or other metal that resists oxidation, is suggested. The so-called concomitant materials in the Colmonoy crystals alloy with the nickel in the surfacing compound and when the surfacing compound is fused to the metal tool, this matrix of nickel and the concomitant materials tends to alloy or otherwise combine with the body of the tool.

While, as has been stated above, a metal base may be surfaced by sweating in the isolated ClBa crystals, or by sweating in the Colmonoy crys- ,tals, we have found such processes less con- Percent Colmonoy crystals -L 95 Pulverized nickel 5 This mixture is fused in a crucible and cooled to a solid, which solid is then pulverized by the action of a crusher followed by a ball mill. The final product may be screened into various grades, the finer grades being desirable for smooth wearresisting surfaces, intermediate grades being se lected for tools, and the coarser grades being useful for abrasive surfaces. 1

That the methods of applying this Colmonoynickel composition arefiexible and its range of uses extensive, may be indicated by examples:

A thin coating resistant to acids and oxidation may be formed by brushing the Colmonoy-nickel composition on the surface of able transient liquid binder and then fusing the Colmonoy product into the metal base by heating with an oxy-acetylene torch. 7

If a heavier case is desired, the initial step may consist incoating the metal base with a sodium silicate solution and then sprinkling the adhesive surface with the composition. If the metal base is heavy it may be preheated in a furnace just prior to application of the crystals with the torch.

A light coat is sufficient to resist wear where the metal base is part of a machine subjected to simple metal-to-metal friction; heavier coats are desirable for cutting tools and drills, for resisting acids, and for lining furnaces to resist high temperatures. Alloy steel tools so surfaced may be subsequently heat treated, the case not interfering with the heat treatment and the heat treatment not aifecting the case.

The Colmonoy-nickel composition when applied as suggested results in a surface having a hardness of approximately 9.

Mild steel may be introduced into the matrix of the resistant coating by placing Colmonoy crystals on the metal base and then heating electrically with a mild steel electrode or using a mild steel welding rod and an oxy-acetylene torch to fuse the mild steel and Colmonoy crys- 40 tals plied to the surface of processes for applying a resistant surface to metal bodies, wehave found it desirable to combine the Colmonoy crystals or the above Colmonoy-nickel composition with any desirable fusible metal to form a welding rod or electrode. The Colmonoy crystals or the Colmonoy-nickel composition may be cast in the body of the rod, or may be incorporated as a core in a tubular metal rod, or may simply be fused to the surface of a rod, or apa rod by means of an adhesive binder. to a metal body, as in a welding process, the metal of the rod modifies the crystalline matrix containing the CrBz crystals, and the resultant matrix fuses, alloys or otherwise combineswith the metal body..

For the purpose of completely disclosing our invention and illustrating the principles involved, we have given specific formulas and detailed methods, but our invention suggests a wide range of formulas and methods and we do not confine ourselves to the precise examples disclosed. We reserve the right to all variations and modificathe base in a suitand concomitant materials,

When such a rod isapplied tionsof our formulas and methods that properly lie within the scope of our appended claims.

Having described our invention, we claim:

1. The chemical compound having the formula CrBz.

2. A composition 0 matter comprising CrBz crystal embedded in a matrix including CrB crystals.

3. CrBa crystals embedded in a matrix of CrB and other concomitant materials produced by the alumino-thermic reduction of intermixed chromium oxides and boron oxides.

4. A composition of matter comprising CrBz crystals in a matrix comprising one or more metals and cm in solid solution.

5. The method of producing a hard crystalline abrasive in a matrix of united crystals of comparable hardness, said method comprising: reducing a chromium oxide and a boron oxide at above 7000 to produce a quantity of CrBz intermixed with a quantity of CrB, and then cooling the mixture to solidification.

6. The method of producing a resistant material, said method comprising igniting a mixture of a chromium oxide, 9. boron oxide, and aluminum to produce a reaction at above 7000 F., cooling the resultant to a solidified mass, and crushing and washing the mass to a residue of CrB, CrBz and concomitant materials.

'I. The method of producing a resistant material, said method comprising igniting a mixture of a chromium oxide, a boron oxide, and aluminum to produce a reaction at above '7000 F., cooling the resultant to a solidified mass, and crushing and washing the mass to a residue of CrBz then digesting out substantially all said concomitant materials to isolate CrBz as the final product.

8. The method of forming and isolating crystals of chromium borlde which consists in mixing chromic anhydrlde, boron trioxide and finely divided aluminum, igniting the mixture and producing by exothermic reaction the said crystals in a matrix including aluminum, dissolving with an acid said matrix and separating the crystals from the acid solvent.

9. The method as set forth in claim 8 in which the mixture to be ignited comprises approximately chromic anhydride 46%, boron trioxide 16% and aluminum 38%.

10. A resistant material comprising CrBa, CrB, and CraBz.

11. A resistant material comprising CrBa and a chromium borlde of lesser boron content than CrBa.

12. A composition of material comprising CrB: crystals embedded in a solid solution including boron and a chromium borlde of lower boron content than CrBz.

13. A method of producing chromium borides that consists in the alumino-thermic reduction of a mixture of CrOa and mm.

' NORMAN W. COLE.

WALTER H. EDMONDS. 

